| Technical
Pamphlet for Workmen - Magneto The early telephones worked on the Magneto system. The telephone was wired to a central
switchboard that would connect the caller to another telephone via cords.
The telephone microphone was powered by a local battery and called the exchange
switchboard by means of a hand generator. The switchboard would also call telephones by
the use of a hand generator. On finishing a call both users would go on hook
and then crank their generators to
signal to the exchange switchboard that they had hung up (this is known as ringing off).
Magneto Telephones
On lines within the same building, the battery-ringing telephone is generally adopted,
owing to its cheapness. On long lines it is necessary to introduce a relay to economise
battery power, and in such circumstances the magneto-ringing telephone is generally
preferred. It will be seen that the transmitter, the primary of the induction coil, and
the speaking battery form a local circuit. This circuit may be closed either by a gravity
switch or a microtelephone press key. With the telephone resting, the magneto bell in
series with a condenser is connected across the lines via the contacts of a switch forming
part of the magneto generator and a second switch forming a portion of the gravity switch.
When the handle of the magneto generator is turned, the bell is disconnected and the
generator is connected across the A and B wires. When the receiver or microtelephone is
removed from its rest, the local speaking circuit is closed, the magneto bell disconnected
from the line, and the receiver in series with the secondary winding of the induction coil
is connected across the A and B wires. The method in which these circuit changes are
effected in the types of telephone instrument used in a magneto system varies
considerably, but the principle remains the same.
GPO Exchange Codes
These are the codes, used in the List of Exchanges, to indicate the type of
equipment in use.
| Type of Exchange
|
1930 |
1936 |
| Magneto, Self-Restoring Indicators |
C |
M |
| Magneto, Hand-Restoring Indicators |
D |
M |
| Magneto, Ring Through System on Lamps |
E |
M |
| Magneto, Hand-Rest., Auto-Clear Indicators/Lamp |
F |
M |
Outgoing Calls
A subscriber calls the exchange by
means of the generator provided for the purpose. On
the call being answered and the connexion to
the called subscriber's line, assuming it is disengaged, being
completed, the two subscribers are enabled to speak.
Power for the transmitters is supplied by local batteries
On the conclusion of conversation, the subscriber, after
replacing the receiver, gives a generator
ring as an indication to the exchange that the call has
terminated and the ringing. current operates an
indicator or relay associated with the
exchange cord connecting circuit.
|